1. Field of the Invention
This invention relates to a sensor which optically detects a fuel mixing ratio of such as, for example, gasoline and alcohol.
2. Description of the Prior Art
A prior art sensor is shown in FIG. 3 in longitudinal cross section. The sensor has a cylindrical casing 104 having an inlet 111 and an outlet 112, the inner space of which forms a chamber for mixing the liquid fuel. Between ends 104a, 104b, is a transparent glass column 101 interfit with O-rings. Light emitting and photo diodes 102, 103 are provided at both ends of the column 101 in operating relationship with each other.
In this structure, the optically refractivity degree of the glass column relative to the liquid fuel changes depending upon the mixing rate of gasoline and alcohol. Light emitted from the diode 102 is totally reflected at the boundary between the column 101 and the liquid fuel and enters diode 103 to generate an output, the value of which is in accordance with the optical intensity. The output thus generated, indicates the mixing ratio of gasoline and alcohol since the relationship between the output and the mixing ratio of gasoline and alcohol has been previously obtained.
However, the O-ring 107 which is usually made from organic material such as plastics or rubber, is somewhat lacking in chemical and physical stability and deteriorates with surface time, leaving room for improvement in positive and long lasting sealing.
Further, the reflection of the light incident upon the boundary between the column 101 and the mixing liquid fuel, is different in intensity depending upon whether it reflects against the liquid fuel or against the portion in which the O-ring 107 positions.
As a result, the light which reflects at the O-ring 107 and falls on the diode 103, is reduced in intensity, so the linear relationship between the refractive index of the mixing liquid fuel and the output of the diode 103, is lost in some degree.
In order to compensate for the loss of the linear relationship, attention has to be in paid to the liquid-tight configuration and dimensional aspects of column 101.
Therefore, it is an object of this invention to provide a sensor with improved liquid-tight configuration, and which is capable of providing a reliable mixing liquid fuel ratio without affecting the liquid-tight configuration and dimensional aspects of the transparent glass column.
According to the invention, a sensor for mixing ratio of liquid fuel comprising, a cylindrical enclosure having both inlet and outlet opening to act as a passage through which the mixing liquid fuel flows, a transparent column concentrically disposed within into the enclosure so that the outer surface contacts the liquid fuel. Each end of the column is inserted into a ring-shaped wall provided within the inner side of the open end portion of the enclosure. A light emitting diode and a photo diode are provided so as to sandwich or bracket the column in the lenghwise direction, so that the light emitted from the former enters the column through its one end and reflects at the boundary of the column with the liquid fuel, and goes to the other end to fall on the photo diode. Metallic sleeve sealants are provided at each end, one side of each of which is tightly telescoped into each end of the column, the other side of which is liquid tightly secured to the outer side of the wall to form a seal between the liquid fuel and the column.